The AM Forum

A local ham inherited an old 6 meter Gonset Communicator. He has been having some intermittent issues with the radio. No surprise. ALL original parts and probably needs some good restoration work. He noted a larger resistor had split apart. R55

R55 in the circuit is a 4 watt carbon comp that supplies B+ to the receiver. The Parts list has it as a 4.7k. The resistor itself has a color code of YELLOW, VIOLET YELLOW which makes it a 470k. Odd. The manual lists two test point for voltages. Y & Z. Z is the input measuring 300v and Y is the output measuring 190v. 110 v drop across the resistor. Works out to 23ma across a 4.7k. That equates to a power dissipation of roughly 2.5 watts. This all seems to work out for a 4.7k.

Really odd to see a 4 watt resistor. Its all black. BIG resistor with color bands but yet the color code is entirely wrong. Odd !

This all making sense or have i been sniffing too many solder fumes ? LOL

With gear that is over 50 years old, it is not uncommon to find 'somebody else's hands' have been in there. Also I will add that just because it is factory assembled rig doesn't mean the person who assembled it didn't make a mistake. Eric, WA4VVI(SK) used a factory built Ranger to excite his CCA transmitter. Duane, KK4AM and I spent the day disassembling the VFO to find that one solder joint inside the VFO enclosure was not soldered! It went 50+ years like this working until one day it gave up the ghost!

No one was in this rig. All original parts. I think the resistor color code may have been misdone when it was made.

What's the model number (4 digits - starts with 3)? They made a II, IIA, IIB (and there was more then one variation with this one). The "II", "IIA", "IIB" were not the model numbers.

You said: "I think the resistor color code may have been misdone when it was made"
What does that even mean?

Asked for model number. Hold please…….

AND > Your statement (?) >> You said: "I think the resistor color code may have been misdone when it was made"
What does that even mean?

You indicated that this resistor split apart which meant it was passing enough current to heat it sufficiently to split. The excessive heat for whatever period of time could have also modified the color of the band.
As an object heats up, it first turns red (color band could have been red from the start as per schematic), then orange (red+yellow light), then yellow. Generally when a resistor heats up badly, the generated energy within the resistor tends to localize and with enough energy buildup, then splits apart. The heat can also modify external colors on the part.

Since it's a carbon resistor, sometimes you can take ohmmeter probes and hook one to one side of the split resistor, and probe the broken side with the probe on the other side and see if you get a reading. Do the same with the other part of the split resistor. If you're lucky, the sum of both resistances will tell you roughly the value of the resistor. Excessive current and heat will probably distort the carbon composition resistance somewhat, but it might give you a clue as to the original resistance.

I resistor reads 8 megohms. Its basically open. Toast

I attached a picture. Take a look

If I wouldn't know any better I would say that it is one of those 'bumble bee' caps.

Nothing like remote troubleshooting.  ::)

You could be right. I have never seen one of those before.

I wish i had the rig here in front of me and a good schematic. Im at a disadvantage here

eBay item number:115415844391

see attached image..

Jim
Wd5JKO

Looks like C70 is a .47 uf “paper” cap in the parts list. C70 is physically close to R55

Making more sense now

Phew ! LOL

The other ham thought it was R55….LOL

Stephanie,

Which component in the photo are you referring to? The one held between two fingers is a cap. Within the  yellow circle is what appears to be a 1 meg resistor, maybe 1w. Is the resistor measuring 8 meg?

Brad K4RT

WX3K said:They have probably caused more problems in radios than Carter has liver pills! Someone decided they could peddle them to the 'audiophool' crowd for absurd prices, (see eBay link!). They claim it enhances the 'tessatura' or some other unknown to mankind aural adjective! Generally, when I find them I cut them out of circuit. They were probably a good idea at the time but a poor application.

Earlier post you stated resistor split. A resistor that's split in two would read infinite resistance.  :)
Carbon composition resistors never open unless they split in two or more pieces :) or you incinerate a internal section of the carbon composition inside the resistor. Hard to do without destroying the body of the resistor.
And as others have pointed out, the part in the picture is a bumble bee type capacitor.  :)

SO, what's next on the agenda  :D

Agenda ? The only agenda i am guilty of is trying to encourage others to dig into old gear like the Gonsets, HA460s, Clegg 66er, etc and put it on the air.

The Gonset we are chatting about has a history. I found it sitting on a shelf of a SK estate. I grabbed it and gifted it to a local ham. He fixed it up and put it on the air for many months. That Gonset had some kick ass sounding AM audio !!!! Unfortunately, the ham became a SK due to COVID. The rig was again gifted to another local ham who had issues with it. Im having a hard time trying to convince the ham to keep it and put it on the air. I will keep trying. It probably needs a Deep dive as far as restorative work.

I have my own projects at the moment. Just finishing up fixing a Clegg 66er i bought. Had some resistors that slide WAY out of tolerance. Slowly getting that rig back in shape. Its the second 66er i have restored to good operating shape. The first is being used by another local ham on our nets.

Love the old gear ! Love operating 6 meter AM

Its my happy place :)

WX3K said:Joe, N3IBX(SK) was going to give me one of his Clegg Zeus transmitters. I purchased a 6M converter for my NC-300 all I really needed was a tower to stick my 5 ele beam on. We were going to use that as our means of full-duplex while chatting on 160M or 75M. A 4X150 modulated by a pair of 811's (Do I have that correct Pete?).is a nice signal stopper on 6M AM. Unfortunately I never found a sufficient tower and Joe passed away before we could get it all together. :'(

Awww. Joe was a good guy. I was so sorry to hear that he passed. I worked him on 6 meters at one point.

Yes ! The Clegg Zeus is a wonderful AM rig ! I use it every week on our 6 meter gathering. Everyone tells me it sounds great. I just smile 😊

I didn't read all the post but the part you pictured is a capacitor

Fred. ka2dzt